If Lyons had turned in a lights-out performance against the Reds, giving him another start would be an easy call. But the 25-year-old pitched just well enough to make the decision just less than obvious about whether he will get the ball Sunday at Pittsburgh.

With Adam Wainwright and Joe Kelly showing good form, and with Shelby Miller apparently returning to good form, and with Lance Lynn battling mightily to regain his good form, fourth-fifths of the Cardinals rotation is set.

But finding a reliable fifth starter remains a challenge for several reasons. Among them are Jake Westbrook’s struggles and bad back, Jaime Garcia’s early-season shoulder surgery, the lack of a trade and the failure of Lyons and numerous other rookies to nail down the job for more than a few starts.

Lyons got a shot against the Reds mainly because three of the Reds’ top four hitters hit from the left side. The 25-year-old Texan’s final line in the 8-6 victory was more impressive than he actually pitched: 5 innings, one earned run, three hits, a walk and seven strikeouts.

But if not for a difficult call by the official scorekeeper, Lyons would have been charged with four earned runs.

With one out and a runner on first in the second, Devin Mesoraco drilled a potential double-play grounder to Daniel Descalso playing shortstop. But the hard-hit ball shot past Descalso and gave the Reds runners on first and third. Eight-hole hitter Zack Cozart promptly tripled in both runs.

After Lyons walked Reds starter Mike Leake, he struck out Shin-Soo Choo for the second out. But Todd Frazier, 1 for 39 against the Cardinals, laced a line drive to right that went for the Reds’ second two-run triple in the inning. By then, the Cardinals trailed 4-0 and Matheny had Carlos Martinez warming up in the bullpen.

Lyons, however, was able to escape the inning with no more runs and went on to work three perfect innings, the kind of rebound success that very well could earn him a start in five days.

“It was about bouncing back and keeping the team in the game as long as possible,” Lyons said. “There was nothing different mechanically. I just started coming after hitters.”

“He was on the ropes,” Matheny said. “He had trouble with getting too much of the plate and against a good lineup, they’re going to make you pay. He really found a nice groove with his sinker and he had good secondary pitches. He just couldn’t control the counts with his fastball.”

Not one to give away his plans for tomorrow, much less next week, Matheny did not address whether Lyons would take the next start. He remains the most likely, though, because of a lack of better options. Check them out:

— Carlos Martinez ended up working two innings in relief of Lyons and, as he did in his start against the Dodgers, impressed with a fastball that reached 99 mph. Still, Martinez was touched for one run in the sixth and very likely would have given up another in the seventh if Jon Jay had not made a sliding catch to take extra bases from Joey Votto with a runner on. Thanks to Allen Craig’s grand slam in the seventh, Martinez ended up with his first big-league win.

Even after Lyons settled down, Matheny continued to have Martinez warm up.

“The more time we give him out there (to warm up in the bullpen), the more chance to get himself ready and get his heart rate down,” Matheny said. “It was nice having them go side by side and having him ready to get us out of a jam if we came into the right-handed part of the lineup.”

— Michael Wacha also was a possibility to start Monday night, based on what general manager John Mozeliak said last week, and could still find his way back into the rotation. Wacha, however, has settled into a relief role since he was called back up earlier this month. Because the 23-year-old is in his first full professional season, it makes sense for the club to let him finish the season without changing his role again.

— Another option would be none of the above. With an off day Thursday, the Cardinals could skip Lyons and go with Joe Kelly on Sunday. Kelly is scheduled to start Tuesday night so he would be on regular rest in the series finale against the Pirates. Matheny, however, said the other day that he wants to use the off day to give his starters an extra day of rest.

— Definitely not an option is Westbrook. Even if he was eligible to return from the disabled list by Sunday — his 15 days aren’t up until til Sept. 7 — he no longer is a lock to start whenever he returns.

— Don’t look outside of the organization for help, either. General manager John Mozeliak the other day lamented the lack of August trades around the majors, citing a shortage of players who have been put on waivers and ridiculous prices for a few who have cleared.

That brings us back to Lyons. To give him a start at pitcher-friendly PNC Park against a struggling lineup makes a lot of sense. But what about the turn after that? Because that also would be against the Pirates, at Busch Stadium, Lyons would have to downright dominate on Sunday to get another start so soon against the same team.

Let’s not get too far ahead, though. Lyons isn’t.

“I’ll come to the field tomorrow and do my work,” he said. “Until I’m told something, I’ll go about my work as if I’m starting another one. If not, we’ll go from there.”

If it were only as easy as he makes it sound.

You can follow Stan McNeal on Twitter at @stanmcneal or email him at stanmcneal@gmail.com